1. Field of the Invention
The present invention relates to an image forming apparatus such as a copier and a printer, a sheet feeding device that feeds a sheet to the image forming apparatus, and a sheet feeding cassette that is removably attached to the sheet feeding device. More particularly, the present invention relates to an image forming apparatus, a sheet feeding device for feeding sheets stacked in a sheet feeding cassette to the image forming apparatus one by one, and a sheet feeding cassette used for such a sheet feeding device.
2. Description of Related Art
Image forming apparatuses such as copiers and printers include a sheet feeding device that feeds sheets for imaging to an image forming part. In general, sheet feeding devices feed sheets from a sheet bundle stacked in a sheet feeding cassette that is removably attached to the sheet feeding device, by delivering sheets one after another by a sheet feeding roller and the like. Among these devices, such a sheet feeding device is known that includes a push-up board for pushing up the stacked sheets in the sheet feeding cassette and thereby bringing the uppermost sheet into contact with a delivery member such as a pick roller.
In such a sheet feeding device, stability is demanded in feeding sheets, regardless of types of sheets or the number of sheets. To meet the demand, many sheet feeding devices employ a friction member at a position opposed to the pick roller to apply friction resistance to the lower layer of a sheet bundle. As the friction member, there have been devised friction members having various shapes or friction coefficients (for example, see Japanese Unexamined Patent Publication No. 2004-210434 and Japanese Unexamined Utility Model Publication No. 6(1994)-18344). In these known publications, it is stated that it is possible to adjust friction force applied to the sheet or contact angle of the sheet and the delivery member so that double-paper feeding can be prevented.